Superregenerative receiver



W. VAN B. ROBERTS SUPERREGENERATIVE RECEIVER Filed June 12, 1931 2 Sheets-Sheet 1 fffD 546K I mam INVENTOR WALTER VAN B. ROBERTS ATTORNEY Feb. 20, 1934. w. VAN B. ROBERTS 1,948,315

SUPERREGENERATIVE RECEIVER Filed June 12, 1931 2 Sheets-Sheet 2 WALTER VAN B ROBERTS BY HQ? ATTORNEY Patented Feb. 20, 1934 UNITED STATES SUPERREGENERATIVE RECEIVER Walter van B. Roberts, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application June 12, 1931. Serial No. 543,925

16 Claims.

The present invention relates to regenerative systems, and more particularly to improved super-regenerative receiving circuits.

In my co-pending application Serial No. 351,411, filed March 36, 1929, there has been disclosed a method of securing great amplification in a super-regenerative system without building up sustained oscillations. Briefly, the method comprised periodically reversing the phase of the feed back in the system for rapidly quenching radio frequency oscillations during the damping period. The specific circuit shown in the aforementioned application consists of a pair of space discharge tubes, one of the tubes intermittently functioning as an oscillation generator, the other tube intermittently and alternately with the first tube acting to quench oscillations prior to the instant when oscillations built up by the oscillation generator would otherwise attain an undesirable amplitude.

Now, I have devised further improved superregenerative circuits embodying the broad principles disclosed in said application, the present circuits, however, including novel, and simplified, arrangements for greatly improving the results heretofore attained.

Accordingly, it may be stated that one of the main objects of my present invention is to provide a method of, and means for, producing superregeneration in a receiving circuit including a pair of oppositely connected space discharge tubes, the method consisting in applying simultaneously both signal energy and a low frequency interrupting voltage in a differential manner to the inputs of said tubes, and coupling the common output circuit of said tubes to the signal input circuit.

Another important object of the present invention is to provide a method of controlling a super-regenerative receiver which consists in causing signals to be regenerated by one means, employing an independent means for degenerating the signals, periodically controlling the relative effectiveness of the two means, and adjusting the degree of super-regeneration by adjusting the length of the period of time during which regenerative action is effective.

Another cbject of the invention is to provide a system including a means for collecting radio frequency signals, a balanced modulator circuit, a relatively low frequency modulating voltage, and means for feeding back to the signal collecting means the side bands at radio frequency produced by modulation.

Still another object of the present invention is to provide an arrangement in a system wherein a balanced modulator circuit, a signal collecting circuit, a relatively low frequency modulating voltage source, and means for feeding back to the signal circuit the side bands at radio frequency produced by modulation is utilized, whereby the amount of side band feed-back isv adjustable, and the strength of side'bands created is controlled. I

Still other objects of the present invention are to improve generally the simplicity and efficiency of super-regenerative receiving circuits, and to particularly provide receiving systems of the super-regenerative type which are not only reliable in operation, but economically manufactured and assembled.

The novel features which Ibelieve to be characteristic of my invention are set forth in particularity in the appended claims, the invention itself, however, as to both its organization and method of operation will best be understood by reference to the following description taken in connection with the drawings in which I have indicated diagrammaticallyseveral circuit arrangements whereby my invention may be carried into effect.

In the drawings,

Fig. 1 diagrammatically shows a circuit embodying the present invention,

Fig. 2 diagrammatically illustrates a modified form of the present invention,

Fig. 3 shows another modification,

Fig. 4 diagrammatically shows still another modification of the invention.

Referring to the accompanying drawings in which like characters of reference indicate the same parts in the different figures, Fig. 1 shows a source of low frequency interrupting current F differentially coupled to the input circuits of a pair of oppositely connected space discharge tubes 1, 2. The source of interrupting current is not shown, and may comprise any type of audio frequency oscillator well known to those skilled in the art, the interrupting frequency preferably having a magnitude of 6700 cycles, source F including means for adjusting the strength of the voltage applied to coil 4. The signal collecting circuit comprises a split inductance-coil including the portions L1, L2, 2. variable condenser C being connected across the said inductance portions. The variable condenser is preferably of the Remler type, and is well known to those skilled in the art as being electrically symmetrical. The grid of each tube is connected to a terminal of each inductance portion,.the remaining terminal of each portion being connected to a terminal of a fixed capacity 3, the latter being connected in series between the portions L1, L2. The fixed capacity 3 is preferably given a value of 0.006 micro-micro-farads, and is connected in shunt with an inductance coil 4, the latter being coupled to a smaller inductance coil 5 which has the source F of low frequency interrupting current connected to it. In practice, the coil 5 is rated at 17.5 milli-henries, while the coil 4 is rated at 114-. milli-henries. About 1.5 volts may be applied across the coil 5. V

Bias is provided for the grids of the tubes by means of an adjustable current source 6, the negative terminal of which source is adjustably connected, as at 'l, to the inductance coil 4, while the positive terminal of said source is connected to the grounded, common, cathode lead of said tubes. In practice it appears that with tubes having an amplification constant of about 9, and 90 volts plate battery, the best bias for the grids of the tubes 1 and 2 lies between 6 and 15 volts, it being pointed out that the larger the bias the stronger should be the audio frequency input.

The anode of each tube has connected in series with it a feed-back inductance coil 8, 8. Positive potential is applied to the anodes of the tubes from a source B, the latter having its negative terminal connected to the cathodes, while its positive terminal is connected in series with each coil 8, 8 through a signal utilization means 9, such as a pair of head phones. A fixed radio frequency icy-pass condenser 10, preferably having a magnitude of about 0.006 micro-micro farads, is connected in parallel to head phones 9. In order to provide regenerative amplification, the coil 8 is coupled for regenerative feed-back to the coil L1, L2, while the coil 8 is also coupled to coilLi, L2, but in such sense as to provide the .reverse feed-back action for rapid quenching of radio frequency oscillations during the damping period, without introducing appreciable damping into the oscillation circuit during the regeneratively amplifying, or building up, period. It has been found that the circuit shown in Fig. 1 operates most efiiciently with well matched tubes. In practice an antenna is not needed, a three inch tuning coil at L1, L2 having been found to supply plenty of signal pick-up. For long wave broadcast stations it is merely necessary to utilize more capacityacross the coil 4, and a correspondingly lower interruption frequency at the source F.

My aforementioned co-pending application disclosed .a super-regenerative receiving circuit wherein the source of interrupting frequency was differentially applied to the common input of a pair of oppositely connected tubes. In the present arrangement both the signal energy and low frequency interrupting energy are diiferentially, and simultaneously, applied to the oppositely connected tubes 1 and 2, and the common output of the two tubes is coupled to the signal input circuit in additive fashion. As explained in the said co-pending application the circuit including the capacity Sand inductance coil 4, is maintained fixedly tuned to the interruptin frequency F. Thus, when the grid of tube 1 is less negativ than normal, the grid of tube 2 is more nega tive than normal. While the grid of tube 2 is very negative, the tube is ineffective. But, it should be noted that the grid of tube 1 is then only slightly negative, and, due to the action of the feed-back coil 8 and the inductance portion L1, the tube 1 builds up oscillations in the radio frequency circuit, the amplitude at a given time depending upon signal input.

Subsequently, the grid of tube 1 becomes very negative, while the grid of tube 2 becomes only slightly negative. This results in the reverse feed-back coil 8, building down or positively quenching the oscillations, thus taking the place of ohmic resistance in quenching oscillations at the interrupting frequency. The advantage of differentially coupling the signal collecting circuit, as well as the interrupting frequency circuit, to the input of tubes 1 and 2 is that stray, or circuit, capacities across the signal tuned circuit may thereby be reduced to a minimum, thus allowing the signal circuit to tune efficiently to very high frequencies.

A modified form of the present invention is shown in Fig. 2 wherein the oppositely connected tubes are provided with a signal collecting circuit differentially connected to the common input of the tubes. As shown in Fig. 2 the source of interrupting frequency F is coupled to the inductance coil 7 by means of the coil 5. In this modification, however, the coupling between the coils 5 and 7 is adjustable, as at M. The anode of each tube is adjustably connected, by means of sliding contacts 11, ll to feed-back coil 8", the latter having one of its terminals connected to the common lead of the cathodes of the tubes through the fixed by-pass condenser 10.

The portions L1 and L2 are provided by split-- ting a single inductance coil at its mid-point, the large inductance coil 7 preferably being tapped near its mid-point as well. The feed-back coil 8 may have the anodes connected to diiierent points thereof, but nevertheless operates efiieiently with both anodes connected to its right hand terminal. The coil 8 is, preferably, permanently fixed with respect to the coil L1, L2, and, for example, may be concentric and coaxial therewith. It is to be noted that the circuit including the large inductance coil 7 and the fixed capacity 3, together with incidental capacities, is maintained fixedly tuned to the interrupting frequency F. Furthermore, the magnitude of the source 6 is preferably, so adjusted as to make the anode currents at both tubes zero, or very small, in the absence of intermediate frequency input.

By adjusting the coupling M the amount of regeneration during alternate half cycles of interrupting frequency is controlled, while counterregeneration during the remaining half cycles is automatically varied proportionally. This type of regeneration control has much less effect on tuning than other methods known in the prior art, as for example the adjustable capacitative coupling between the plate and resonant input circuit of a tube amplifier.

If desired, an antenna circuit may be employed in conjunction with the signal input circuit, the antenna circuit being conventionally represented as including capacities 13, 13' in series with each inductance portion L1, L2.

It will be seen that in Fig. 2 there has been shown a method of controlling super-regeneration which consists in causing signals to be regenerated by one means, and to be degenerated by another means, the relative effectiveness of the two means being periodically switched, while, by means of the adjustable coupling M, the amount of shift of relative effectiveness is utilized for controlling the strength of regeneration.

The arrangement shown in Fig. 2 may also be lei explained as comprising a balanced -modulator circuit wherein there is employed a means for collecting radio frequency signal energy, and a relativelylow frequency modulating voltage supplied by a source F, the coil 8 functioning for feeding back to the radio frequency signal circuit the side bands at radio frequency produced by modulation. That such a balanced modulator circuit is involved in the arrangement shown in Fig. 2 may be demonstrated from the following considerations:

With an exact mid-tap on coil 7, the voltages impressed on the grids of the two tubes are:

On grid of tube (1) a voltage -.K-}- E's-| EF On grid of tube (2") a voltage K- /2Es- /2EF. The expression K denotes the constant negative potential due to the control grid biasing potential source 6 in Fig. 2. The term Es denotes the potential due to the signal energy. The term EF denotes the potential due to the source of interruption frequency energy of frequency F.

Now the plate currents may be expressed as power series of grid voltages. If the taps ll, 11 are both at the right hand end of the coil, the signal frequency currents, and the interruption frequency currents will both cancel in coil 8". But due to the second order term, currents representing the product ESEF will flow from both tubes through 8" in like phase. These currents include currents of frequencies fsiF, that is, the side bands generated by the modulation of a signal by the low frequency Fig. 2 shows a means for feeding back these side bands without feeding back the signal frequency.

Therefore, Fig. 2 may be described as showing a balanced modulator circuit whose output side bands are coupled back to its input high frequency circuit.

A further modification, involving a simplified circuit structure, is shown in Fig. 3. This modified form of construction does not employ an inductive coupling between the source of interrupting frequency F and the common input of the tubes 1, 2, but instead the source F is directly connected across the fixed capacity 3. In order to control the relative bias applied to the grids of the tubes 1, 2 the negative terminal of the grid biasing source 6 is adiustably connected, as at 20 to a fixed resistor 21. The latter, preferably, has a magnitude of about 20,000 ohms, the resistor being shunted across the condenser 3.

It will, also, be noted that in this simplified form of the invention the feed back coil 8" is connected in series between the utilization means 9 and the anode of each tube, the anodes being permanently connected to the right hand terminal of coil 8". The advantages obtained by this construction are as follows:

(1) Adjustment of tuning condenser C does not upset the tuning of the circuit tuned to the interrupting frequency F.

2) A simple adjustment of slider 20 balances up any tube inequalities, or allows a deliberate unbalance in favor of either tube if desired.

(3) The amount of apparatus is reduced.

It is, of course, understood that the amount of super-regeneration may be controlled by varying the coupling of coil 8" to coil L1, L2 by varying the voltage of bias source 6, or by varying the amount of voltage output of source F.

The modification shown in Fig. 4 comprises a differentially connected signal input circuit which however does not require a split coil, but a coil L3. The diiferentially applied interruption voltage is, in this case, applied in the plate circuit through transformer M1. The secondary 30 of thelatter is shunted by radiofreq'uencyby-pass series condensers 31, 32. The action'is the same as in Fig. 3 'except'that a greater voltage must be applied in the plate circuit to cause as great a change in the amounts of feed back of the tubes than when applied in the grid circuit. The advantage possessed by the modification in-Fig. l lies chiefly in the simplificationof the input circuit and the signal frequency tuning coil system.

While I have indicatedand described several systems for carrying my invention into effect, it will be apparent to one skilled in the art that my invention is by no means limited to the particular organizations shown and described, but that many modifications may be made without 'departing from the scope of -my invention as set forth in the appended claims.

What I claim is:

1. In combination, in a super-regenerativereceiver, a pair of oppositely connected spacedischarge tubes having a common input and output circuit, a signal circuit, an interrupting frequency source, said signal circuit and source being differentially connected to the input circuit of said tubes, the common output circuit'of said tubes being coupled to said signal circuit.

2. In combination, in a super-regenerative receiver, a pair of oppositely connected space discharge tubes having a common input and output circuit, a signal circuit, an interrupting frequency source, said signal circuit and source being differentially connected to the input circuit of said tubes, the common output circuit of said tubes being differentially coupled to said signal circuit.

3. The method of controlling a super-regenerative receiver which consists in collecting signal energy, differentially applying the energy to the input circuits of a pair of space discharge tubes, regenerating the signals by one of said tubes, degenerating the signals by the other tube, periodically switching the relative effectiveness of the two tubes, and controlling the strength of super-regeneration by the amount of shift of said relative effectiveness.

4. In combination, means for collecting radio frequency signals, a balanced modulator circuit having its input coupled to the signal collecting means, a source of relatively low frequency modulating voltage coupled to said circuit, and means for feeding back from the circuit output to said signal collecting means the side bands at radio frequency produced by modulation.

5. In combination, means for collecting radio frequency signals, a balanced modulator circuit having its input coupled to the signal collecting means, a source of relatively low frequency modulating voltage coupled to said circuit, and means for feeding back from the circuit output to said signal collecting means the side bands at radio frequency produced by modulation, and means for adjusting the amountof feed back of said side bands.

6. In combination, means for collecting radio frequency signals, abalanced modulator circuit having its input coupled to the signal collecting means, a source of relatively low frequency modulating voltage coupled to said circuit, and. means for feeding back from the circuit output to said signal collecting means the side bands at radio frequency produced by modulation, and means iao for controlling the strength of side bands pro- ,7

duced.

7. The combination of a pair of tubes provided with input and output circuits, a signal circuit differentially connected to the input circuits of said tubes, means for diiferentially applying a relatively low frequency voltage between a cold electrode of one tube and a cold electrode of the other tube, and means for feeding back energy from the output circuits of the tubes to the said signal circuit.

8. In a super-regenerative receiverya pair of electron discharge tubes having input and out- .put circuits, the two input circuits having a common portion including a tuned circuit and the two output circuits having a common portion including a load circuit, a source of signal energy connected to said common tuned circuit, to impress signal energy upon the input circuits of said tubes in unlike sense, a source of interruption frequency waves diilerentially coupled to both said input circuits, means for coupling the output circuit of one of said tubes to its input circuit in a regenerative sense, and means for coupling the output and input circuits of the other tube in a degenerative sense.

9. In a super-regenerative receiver, a pair of electron discharge tubes having input and output circuits, the two input circuits having a common portion including a tuned circuit and the two output circuits having a common portion including a load circuit, a source of signal energy connected to said common tuned circuit, to impress signal energy upon the input circuits of said tubes in unlike sense, a source of intenruption frequency waves differentally coupled to both said output circuits, means for coupling the output circuit of one of said tubes to its input circuit in a regenerative sense, and means for coupling the output and input circuits of the other tube in a degenerative sense.

10. In a super-regenerative receiver, a of electron discharge tubes having input and output circuits, the two input circuits having a common portion including a tuned circuit and the two output circuits having a common portion including a load circuit, a source of signal energy connected to said common tuned circuit, to impress signal energy upon the input circuits of said tubes in unlike sense, a source of interruption frequency waves difierentially coupled to both said input circuits, means for coupling the output circuit of one of said tubes to its input circuit in a regenerative sense, and means for coupling the output and input circuits of the other tube in a degenerative sense and means for varying the coupling between said interruption frequency source and said input circuits.

11. In a super-regenerative receiver, a pair of electron discharge tubes having input and output circuits, the two input circuits having a common portion including a tuned circuit and the two output circuits having a common portion including a load circuit, a source of signal energy connected to said common tuned circuit, to impress signal energy upon the input circuits of said tubes in unlike sense, a source of interruption frequency waves differentially coupled to both said input circuits, means for coupling the output circuit of one of said tubes to its input circuit in a regenerative sense, and means for coupling the output and input circuits of the other tube in a degenerative sense, said last two mentioned means consisting of a single coil connected to both said output circuits.

12. In a super-regenerative receiver, a pair of electron discharge tubes having input and output circuits, the two input circuits having a common portion including a tuned circuit and the two output circuits having a common portion including a load circuit, a source of signal energy connected to said common tuned circuit, to impress signal energy upon the input circuits of said tubes in unlike sense, a source of interruption frequency waves differentially coupled to both said input circuits, means comprising an inductance coil for coupling the output circuitv of one of said tubes to its input circuit in a regenerative sense, and means comprising the said coil for coupling the output and input circuits of the other tube in a degenerative sense,

said output circuits being variably connected to said coupling coil.

13. In a super-regenerative receiver, a pair of electron discharge tubes, a resonant circuit, including means for tuning the latter through a signal frequency range, connected to the signal control grids of the tubes, a connection between the anodes of said tubes, said connection including at least one coil regeneratively coupled to said resonant input circuit, and a source of interruption frequency energy coupled to the said connection.

14. In a super-regenerative receiver, a pair of electron discharge tubes, a resonant circuit, including means for tuning the latter through a signal frequency range, connected to the signal control grids of the tubes, a connection between the anodes of said tubes, said connection including at least one coil regeneratively coupled to said resonant input circuit, and a source of interruption frequency energy differentially coupled to the said connection.

15. In a super-regenerative receiver, a pair of electron discharge tubes, a resonant circuit, including means for tuning the latter through a signal frequency range, connected to the signal control grids of the tubes, a connection between the anodes of said tubes, said connection including one coil regeneratively coupled to said resonant ,input circuit, and a source of interruption frequency energy of audible frequency, differentially coupled to the said connection.

16. In a super-regenerative receiver, a pair of tubes, a tunable signal circuit connected to the control grids of both tubes, 2. common output circuit connected to the anodes of both tubes, said common output circuit includin only a single coil coupled to the tunable circuit, and a source of interruption frequency energy differentially coupled to the said control grids.

VJALTER VAN B. ROBERTS.

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